Napoli rout Livorno, Verona move up
Besides keeping Napoli two points behind Roma, which it faces next, the victory also helped the southern squad move on from a 2-0 midweek defeat to Arsenal in the Champions League.
Goran Pandev put Napoli ahead three minutes in at the San Paolo stadium, Gokhan Inler doubled the lead in the 26th, Jose Callejon added another in the 54th and Marek Hamsik scored his fifth of the season in the 83rd.
Pandev finished off a counterattack after getting set up by Belgium midfielder Dries Mertens and Inler found the target with a long and powerful shot that Livorno goalkeeper Francesco Bardi should have stopped.
Callejon scored from within the area after getting set up by Pandev and Hamsik finished off another swift counterattack that followed a Livorno corner by knocking in a rebound.
Napoli entered the weekend tied for second with Juventus, which was hosting AC Milan later in a serious test of its title hopes.
On Saturday, Francesco Totti scored twice as Roma won 3-0 at Inter Milan to extend its winning start in Serie A to seven matches. The Giallorossi have scored 20 goals and conceded just one.
In Sunday's other matches, it was: Bologna 1, Hellas Verona 4; Catania 1, Genoa 1; Parma 3, Sassuolo 1; Sampdoria 2, Torino 2; and Udinese 2, Cagliari 0.
Hellas Verona, back in the top division for the first time in 11 years, moved into fifth place, eight points behind Roma, after getting goals from Fabrizio Cacciatore, Juan Manuel Iturbe, former Italy forward Luca Toni and Jorginho.
The start of the match was delayed for 20 minutes because Verona's bus was held up by fan clashes outside the stadium.
Antonio Cassano, another former Italy forward, scored one goal and set up two others as 10-man Parma won a regional derby.
A minute of silence was observed before each match to mourn the 100-plus African migrants killed in a shipwreck off the Italian island of Lampedusa on Thursday.